Today, the performance and functions in electronic devices improve rapidly. Accordingly, the electromagnetic waves emitted from individual electronic devices or electronic circuits strengthen. When an electronic device or electronic circuit emits strong electromagnetic waves, the electromagnetic waves may cause a surrounding electronic device or electronic circuit to operate erroneously.
As one of factors that cause emission of strong electromagnetic waves, an unwanted high-frequency current flowing through the circuit, particularly a high-frequency noise current flowing through the power supply wiring line of a semiconductor device, is known. To suppress the high-frequency noise current by design or at an early stage of the manufacture is sought for.
Measurement of a magnetic near-field intensity allows to specify the path of the high-frequency noise current by non-contact inspection. This enables verification of the effect of suppressing the high-frequency noise current at an early stage of design or the manufacture, making it possible to take measures against electromagnetic waves. As sensors of a type that detect a magnetic field by measuring an electromotive force induced in a coil, for example, the following sensors are known.
According to the structure of the magnetic field sensor described in Japanese Patent Laid-Open No. 10-82845 (reference 1), each of a pair of dielectric wiring substrates having C-shapes is provided with a ground conductor having such a shape and size that it overlaps the corresponding dielectric wiring substrate when seen from the top. The pair of dielectric wiring substrates sandwich a strip conductor having a predetermined shape. A voltage induced between the starting end position of the strip conductor and each ground conductor is detected as a magnetic field detection output.
The dielectric wiring substrates in this magnetic field sensor are arranged to oppose each other such that the ground conductors are exposed on their outer surfaces. The strip conductor electrically connects to the respective ground conductors at the terminal end position of the strip conductor. Each ground conductor serves to shield the strip conductor from the external electric field. The terminal end position of the strip conductor is located on one of those two ends of the dielectric wiring substrates which oppose each other through a gap (a notch that forms a C shape). The strip conductor extends from the terminal end position across the gap along one of the C-shaped semicircular peripheral portions of the dielectric substrates, and starts at a predetermined position on the semicircular peripheral portion.
According to the structure of the magnetic field sensor described in Japanese Patent Laid-Open No. 2000-171535 (reference 2), the first, second, and third layers respectively having conductor patterns with predetermined shapes are stacked such that insulating layers are interposed between the respective layers and that the conductor pattern of the second layer connects to the conductor patterns of the first and third layers. A voltage generated in a load connected between the conductor pattern of the second layer and the conductor pattern of the first layer, and a voltage generated in a load connected between the conductor pattern of the second layer and the conductor pattern of the third layer are detected as a magnetic field output. In this magnetic field sensor, the shape of each conductor pattern is so selected as to form a 1-turn loop coil when the conductor pattern is seen from the top. The conductor patterns of the first and third layers serve to shield the conductor pattern of the second layer from the external electric field.
According to the structure of the pen type magnetic near-field probe described in Japanese Patent Laid-Open No. 2000-121712 (reference 3), a printed wiring board (support) having a fine loop coil, transmission line, and high-frequency cable connecting portion connects to the distal end of a retainer.
In the tightly fixed magnetic near-field probe described in Japanese Patent Laid-Open No. 2000-147034 (reference 4), a 1-turn loop coil, coplanar transmission line, and high-frequency connector are arranged on a sheet-like substrate. A releasable adhesion surface is formed on the rear surface of the substrate, or an engaging portion engageable with a wire is formed on the substrate. Thus, the probe can be adhered to and released from a measurement target.
According to the structure of the magnetic near-field probe described in Japanese Patent Laid-Open No. 2003-207531 (reference 5), a 1-turn loop coil and a transmission circuit connecting to it are provided to a dielectric. The impedance of the transmission circuit is gradually changed in the transmission direction to suppress a decrease in output voltage.